1. Field of the Invention
This invention relates to electrochemical production of alkali alcoholates from alkali metal salt solutions and alcohol by using an ion conducting ceramic solid electrolyte or membrane based electrochemical cell. In preferred embodiments, it includes making sodium methylate (i.e. sodium methoxide) in an electrolytic cell using ceramic membranes. In preferred embodiments, the process includes the use of sodium-ion conducting ceramic membranes.
2. Description of the Related Art
There are two primary methods of making sodium methylate, also called sodium methoxide that are in current use. The first is a sodium-based process in which sodium metal is reacted with methanol to produce sodium methylate. This method uses sodium metal as a raw material, which is expensive and it reacts violently with lower alcohols and the process can be extremely difficult to control. Sodium metal also reacts violently with water requiring elaborate and expensive equipments and systems for storage, handling, and delivery of sodium metal.
In a second process, sodium methylate is made from sodium amalgam produced from the chlor alkali electrolysis in a mercury cell by reacting with the amalgam with alcohol. The drawback of this process is it can result in the contamination of the product and the environment with mercury, a well known carcinogen. For this reason, use of sodium methylate produced by this method will likely be unattractive for agriculture, pharmaceuticals, and bio-diesel applications.
In certain electrolytic systems for use in producing alkali alcoholates from salt solutions, various materials have been suggested for use as an ion-conducting membrane positioned between the anolyte and catholyte chambers for transportation of ions there through. Such materials include ceramic materials alone, polymeric materials, and combinations of ceramic and polymeric materials
The known advantage of polymeric materials as electrolytes in the electrolysis of salt solutions is their high conductivity and increased high resistance to acidic and caustic environments resulting from the electrolytic process. The known disadvantage of polymers, however, is their low selectivity for ionic species; that is, along with the desired alkali metal ions, polymers transport unwanted protons & cations and also cause the electroosmotic transport of water, the result of which is an inefficient operation of the electrolytic cell.
Use of materials such as βI and βII-Alumina membranes reported by Horn (U.S. Patent Application Publication No. 2003/0106805) for synthesis of alkali alcoholates show low sodium ion conductivity at temperatures below 100° C., the temperature range most practical for aqueous electrochemical applications. In Horn's patent application, the electrochemical performance of the cell decays or degrades with time due to the degradation of the conducting structure of membrane, which limits ionic conductivity in βI and βII-alumina electrolyte at temperatures below 100° C. A considerable increase in voltage of the cell was reported in Horn's application where the cell performance degraded after 4 hours of operation. The current density decreased from 40.8 A/m2 to 7.5 A/m2 during this period in one of the tests. Such a low current density, 0.75 mA/cm2 for his cell, would require an extremely large number of cells for a commercial operation, making it impractical to commercialize the technology based on βI and βII-alumina membranes. The complexity of processing βI and βII-alumina materials and their high manufacturing cost, aided with stability issues in aqueous salts precursors makes the βI and βII-alumina less practical for this intended application. Horn reports the application of an ion permeable layer deposited by vapor depositions method on the solid electrolyte, to limit the solid electrolyte from reacting with the aqueous anolyte solutions Data reported in the Horn application refers to back-migration of methanol into the anolyte solution, causing its contamination and adversely impacting its eventual disposal. There is no reported data in the Horn application that shows sodium methylate of 25 wt. % concentration or above could be produced by his cell.